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Arctic Saw Fastest August Sea Ice Retreat On Record

Arctic Saw Fastest August Sea Ice Retreat On Record

Following
a record-breaking season of arctic sea ice decline in 2007, NASA
scientists have kept a close watch on the 2008 melt season. Although
the melt season did not break the record for ice loss, NASA data are
showing that for a four-week period in August 2008, sea ice melted
faster during that period than ever before.

Each year at the end
of summer, sea ice in the Arctic melts to reach its annual minimum. Ice
that remains, or "perennial ice," has survived from year to year and
contains old, thick ice. The area of arctic sea ice, including
perennial and seasonal ice, has taken a hit in past years as melt has
accelerated. Researchers believe that if the rate of decline continues,
all arctic sea ice could be gone within the century.

"I was not
expecting that ice cover at the end of summer this year would be as bad
as 2007 because winter ice cover was almost normal," said Joey Comiso
of NASA's Goddard Space Flight Center in Greenbelt, Md. "We saw a lot
of cooling in the Arctic that we believe was associated with La NiÃ±a.
Sea ice in Canada had recovered and even expanded in the Bering Sea and
Baffin Bay. Overall, sea ice recovered to almost average levels. That
was a good sign that this year might not be as bad as last year."

The
2008 sea ice minimum was second to 2007 for the record-lowest extent of
sea ice, according to a joint announcement Sept. 16 by NASA and the
University of Colorado's National Snow and Ice Data Center (NSIDC) in
Boulder, Colo. As of Sept. 12, 2008, the ice extent was 1.74 million
square miles. That's 0.86 million square miles below the average
minimum extent recorded from 1979 to 2000, according to NSIDC.

Contributing
to the near-record sea ice minimum in 2008 was a month-long period in
the summer that saw the fastest-ever rate of seasonal retreat during
that period. From August 1 to August 31, NASA data show that arctic sea
ice extent declined at a rate of 32,700 square miles per day, compared
to a rate of about 24,400 square miles per day in August 2007. Since
measurements began, the arctic sea ice extent has declined at an
average rate of 19,700 miles per day at the point when the extent
reaches its annual minimum.

Observations of changes to sea ice
over time are possible due to a 30-year record of data from NASA and
other agency satellites, including Nimbus-7, Aqua, Terra and the Ice,
Cloud, and land Elevation Satellite (ICESat).

Researchers say
that the recent seasonal acceleration could be in part due to
conditioning going on in the Arctic. For example, research by Jennifer
Kay of the National Center for Atmospheric Research in Boulder, Colo.,
and colleagues reported this April in Geophysical Research Letters that
reduced cloud cover in 2007 allowed more sunlight to reach Earth,
contributing to a measureable amount of sea ice melt at the surface.
Reduced cloud cover also contributed to warmer ocean surface
temperatures that led to melting of the ice from below.

"Based
on what we've learned over the last 30 years, we know that the
perennial ice cover is now in trouble," Comiso said. "You need more
than just one winter of cooling for the ice to recover to the average
extent observed since the measurements began. But the trend is going
the other way. A warming Arctic causes the surface water to get warmer,
which delays the onset of freeze up in the winter and leads to a
shorter period of ice growth. Without the chance to thicken, sea ice
becomes thinner and more vulnerable to continued melt."